This invention relates to radiotelephone communications systems and methods, and more particularly to terrestrial cellular and satellite cellular radiotelephone communications systems and methods.
Satellite radiotelephone communications systems and methods are widely used for radiotelephone communications. Satellite radiotelephone communications systems and methods generally employ at least one space-based component, such as one or more satellites that are configured to wirelessly communicate with a plurality of satellite radiotelephones.
A satellite radiotelephone communications system or method may utilize a single antenna beam covering an entire area served by the system. Alternatively, in cellular satellite radiotelephone communications systems and methods, multiple beams are provided, each of which can serve distinct geographical areas in the overall service region, to collectively serve an overall satellite footprint. Thus, a cellular architecture similar to that used in conventional terrestrial cellular radiotelephone systems and methods can be implemented in cellular satellite-based systems and methods. The satellite typically communicates with radiotelephones over a bidirectional communications pathway, with radiotelephone communication signals being communicated from the satellite to the radiotelephone over a downlink or forward link, and from the radiotelephone to the satellite over an uplink or return link.
The overall design and operation of cellular satellite radiotelephone systems and methods are well known to those having skill in the art, and need not be described further herein. Moreover, as used herein, the term xe2x80x9cradiotelephonexe2x80x9d includes cellular and/or satellite radiotelephones with or without a multi-line display; Personal Communications System (PCS) terminals that may combine a radiotelephone with data processing, facsimile and/or data communications capabilities; Personal Digital Assistants (PDA) that can include a radio frequency transceiver and a pager, Internet/intranet access, Web browser, organizer, calendar and/or a global positioning system (GPS) receiver; and/or conventional laptop and/or palmtop computers or other appliances, which include a radio frequency transceiver.
Terrestrial networks can enhance cellular satellite radiotelephone system availability, efficiency and/or economic viability by terrestrially reusing at least some of the frequency bands that are allocated to cellular satellite radiotelephone systems. In particular, it is known that it may be difficult for cellular satellite radiotelephone systems to reliably serve densely populated areas, because the satellite signal may be blocked by high-rise structures and/or may not penetrate into buildings. As a result, the satellite spectrum may be underutilized or unutilized in such areas. The use of terrestrial retransmission can reduce or eliminate this problem.
Moreover, the capacity of the overall system can be increased significantly by the introduction of terrestrial retransmission, since terrestrial frequency reuse can be much denser than that of a satellite-only system. In fact, capacity can be enhanced where it may be mostly needed, i.e., densely populated urban/industrial/commercial areas. As a result, the overall system can become much more economically viable, as it may be able to serve a much larger subscriber base. Finally, satellite radiotelephones for a satellite radiotelephone system having a terrestrial component within the same satellite frequency band and using substantially the same air interface for both terrestrial and satellite communications can be more cost effective and/or aesthetically appealing. Conventional dual band/dual mode alternatives, such as the well known Thuraya, Iridium and/or Globalstar dual mode satellite/terrestrial radiotelephone systems, may duplicate some components, which may lead to increased cost, size and/or weight of the radiotelephone.
One example of terrestrial reuse of satellite frequencies is described in U.S. Pat. No. 5,937,332 to the present inventor Karabinis entitled Satellite Telecommunications Repeaters and Retransmission Methods, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein. As described therein, satellite telecommunications repeaters are provided which receive, amplify, and locally retransmit the downlink signal received from a satellite thereby increasing the effective downlink margin in the vicinity of the satellite telecommunications repeaters and allowing an increase in the penetration of uplink and downlink signals into buildings, foliage, transportation vehicles, and other objects which can reduce link margin. Both portable and non-portable repeaters are provided. See the abstract of U.S. Pat. No. 5,937,332.
In view of the above discussion, there continues to be a need for systems and methods for terrestrial reuse of cellular satellite frequencies that can allow improved reliability, capacity, cost effectiveness and/or aesthetic appeal for cellular satellite radiotelephone systems, methods and/or satellite radiotelephones.
Some embodiments of the present invention allow a satellite radiotelephone frequency to be reused terrestrially within the same satellite cell, while allowing intra-system interference to be reduced. In particular, some of these embodiments include a space-based component, such as a satellite, that is configured to receive wireless communications from a first radiotelephone in a satellite footprint, comprising one or more cells, over a satellite radiotelephone frequency band. An ancillary terrestrial network, comprising one or more ancillary terrestrial components, is configured to receive wireless communications from a second radiotelephone in the satellite footprint over the satellite radiotelephone frequency band. The space-based component also receives the wireless communications from the second radiotelephone in the satellite footprint over the satellite radiotelephone frequency band as interference, along with the wireless communications that are received from the first radiotelephone in the satellite footprint over the satellite radiotelephone frequency band. An interference reducer is responsive to the space-based component and to the ancillary terrestrial network, and is configured to reduce the interference from the wireless communications that are received by the space-based component from the second radiotelephone in the satellite footprint over the satellite radiotelephone frequency band, using the wireless communications that are received by the ancillary terrestrial network from the second radiotelephone in the satellite footprint over the satellite radiotelephone frequency band.
In other embodiments, the ancillary terrestrial network is closer to the first and second radiotelephones than is the space-based component, such that the wireless communications from the second radiotelephone are received by the ancillary terrestrial network prior to being received by the space-based component. In these embodiments, the interference reducer is configured to generate at least one delayed replica of the wireless communications from the second radiotelephone that are received by the ancillary terrestrial network and to subtract the delayed replica of the wireless communications from the second radiotelephone that are received by the ancillary terrestrial network, from the wireless communications that are received from the space-based component. Adaptive interference-canceling techniques, for example Least Mean Squared Error (LMSE), Kalman, zero-forcing and/or various variations thereof, can be used to update the coefficients of transversal filters to provide adaptive interference reduction. Thus, an entire band of satellite frequencies may be reused terrestrially within any given satellite cell, according to these embodiments of the invention.
Other embodiments of the invention can provide a reconfigurable (multiple-mode) ancillary terrestrial component, that operates conventionally in a first mode, and that operates in a second mode to reduce interference by the ancillary terrestrial component with other, out of band, satellite-based systems, such as GPS/GLONASS systems. As is well known to those having skill in the art, GPS and GLONASS are satellite-based systems that can be used to measure positions on earth.
In particular, these embodiments of radiotelephone systems and methods include a space-based component that is configured to receive wireless communications from radiotelephones over a first range of satellite band return link frequencies and to transmit wireless communications to the radiotelephones over a second range of satellite band forward link frequencies that are spaced apart from the first range. A multiple mode ancillary terrestrial component is selectively configured to receive wireless communications from the radiotelephones over the first range of satellite band return link frequencies and to transmit wireless communications to the radiotelephones over the second range of satellite band forward link frequencies that is spaced apart from the first range, in a first mode of operation. In a second mode of operation, wireless communications are transmitted to the radiotelephones by the ancillary terrestrial component over a modified second range of satellite band forward link frequencies. In some embodiments, the modified second range of satellite band forward link frequencies is selected to reduce interference with wireless receivers that operate outside the second range of satellite band forward link frequencies, compared to operation of the ancillary terrestrial component, using the second range of satellite band forward link frequencies.
As will be described below, many embodiments of modified second ranges of satellite band forward link frequencies may be used by multiple mode ancillary terrestrial components. Moreover, the modified second ranges of satellite band forward link frequencies may be used by a single mode ancillary terrestrial component, to reduce and preferably eliminate interference by the forward link of the ancillary terrestrial component with other satellite-based systems, such as GPS/GLONASS systems. Finally, as also will be described below, in some embodiments, the multiple mode or single mode ancillary terrestrial component also is selectively configured to receive wireless communications from the radiotelephones over a modified first range of satellite band return link frequencies.
More specifically, in some embodiments, the modified second range of satellite band forward link frequencies includes only a subset of the second range of satellite band forward link frequencies, so as to provide a guard band within the second range of satellite band forward link frequencies that is not used to transmit wireless communications from the ancillary terrestrial component to the radiotelephones. In other embodiments, the modified second range of satellite band forward link frequencies includes only a subset at a low frequency portion of the second range of satellite band forward link frequencies, so as to provide a guard band at a high frequency portion of the second range of satellite band forward link frequencies that is not used to transmit wireless communications from the ancillary terrestrial component to the radiotelephones. In still other embodiments, the first range of satellite band return link frequencies is contained in the L-band of frequencies above GPS/GLONASS frequencies, and the second range of satellite band forward link frequencies is contained in the L-band of frequencies below the GPS/GLONASS frequencies. The modified second range of satellite band forward link frequencies includes only a portion of the second range of satellite band forward link frequencies that is remote from the GPS/GLONASS frequencies, so as to provide a guard band in a portion of the second range of satellite band forward link frequencies that is adjacent the GPS/GLONASS frequencies.
In other embodiments, the ancillary terrestrial component also is selectively configured to receive wireless communications from the radiotelephones over a modified first range of satellite band return link frequencies that includes at least one time division duplex frequency that is used to transmit wireless communications to the radiotelephones and to receive wireless communications from the radiotelephones at different times. In yet other embodiments, the at least one time division duplex frequency comprises a frame including a plurality of slots, where at least a first one of the slots is used to transmit wireless communications to the radiotelephones and wherein at least a second one of the slots is used to receive wireless communications from the radiotelephones. In yet other embodiments, the entire first range of satellite band return link frequencies is time division duplexed to transmit wireless communications to the radiotelephones and to receive wireless communications from the radiotelephones at different times. In still other embodiments, a first number of slots is used to transmit wireless communications to the radiotelephones, and a second number of slots is used to receive wireless communications from the radiotelephones, wherein the first number is greater than the second number. In still further embodiments, at least a first one of the slots is used to transmit wireless communications to the radiotelephones using a first modulation and/or protocol such as EDGE modulation and/or protocol, and at least a second one of the slots is used to receive wireless communications from the radiotelephones using a second modulation and/or protocol such as GPRS modulation and/or protocol, wherein the first modulation and/or protocol is more spectrally efficient than the second modulation and/or protocol.
In yet other embodiments of the invention, interference with out-of-band satellite systems, such as GPS/GLONASS, can be reduced by using a modified second range of satellite band forward link frequencies that includes a plurality of frequencies in the second range of satellite band forward frequencies that are transmitted by the ancillary terrestrial component to the radiotelephones at a power level, such as a maximum power level, that monotonically decreases as a function of frequency. In still other embodiments, only a subset of frequencies at a first or second end of the second range of satellite band forward link frequencies is transmitted at a power level, such as a maximum power level, that monotonically decreases toward the first or second end of the second range of satellite band forward link frequencies. More specifically, in some embodiments, when the first range of satellite band return link frequencies is contained in the L-band of frequencies above GPS/GLONASS frequencies and the second range of satellite band forward link frequencies is contained in the L-band of frequencies below the GPS/GLONASS frequencies, the modified second range of satellite band forward linked frequencies includes a subset of frequencies proximate to an end of the second range of satellite band forward link frequencies adjacent the GPS/GLONASS frequencies that are transmitted by the ancillary terrestrial component of the radiotelephones at a power level, such as a maximum power level, that monotonically decreases towards the end of the second range of satellite band forward link frequencies adjacent the GPS/GLONASS frequencies.
In still other embodiments, the plurality of frequencies in the second range of satellite band forward link frequencies are transmitted by the ancillary terrestrial component to the radiotelephones as a function of a distance of the respective radiotelephone from the ancillary terrestrial component and at a power level, such as a maximum power level, that monotonically decreases as a function of frequency. Thus, the lower power levels may be associated with the higher frequencies and may be used to communicate with radiotelephones that are closer to the ancillary terrestrial component and the higher power levels may be associated with the lower frequencies and may be used to communicate with radiotelephones that are further from the ancillary terrestrial component.
In other embodiments of the present invention, interference with other satellite receiver systems by the ancillary terrestrial component can be reduced or prevented by leaving at least two contiguous slots in the frame that is transmitted by the ancillary terrestrial component to the radiotelephones unoccupied. In yet other embodiments, at least three contiguous slots are left unoccupied. In still other embodiments, at least two contiguous slots in the frame are transmitted at lower power than remaining slots in the frame that is transmitted by the ancillary terrestrial component to the radiotelephones. In still further embodiments, three contiguous slots in the frame are transmitted at lower power than remaining slots in the frame that is transmitted by the ancillary terrestrial component to the radiotelephones. In still other embodiments, the at least two or three contiguous slots that are transmitted at lower power are transmitted to radiotelephones that are relatively close to the ancillary terrestrial component, whereas the remaining slots are transmitted to radiotelephones that are relatively far from the ancillary terrestrial component. In still other embodiments, only frequencies that are proximate to the first or second end of the second range of satellite band forward link frequencies are transmitted by the ancillary terrestrial component to the radiotelephones with at least two contiguous slots being unoccupied or transmitted at reduced power.
In other embodiments of the invention, a multiple mode ancillary terrestrial component is selectively configured to receive wireless communications from the radiotelephones over a first range of satellite band return link frequencies, and to transmit wireless communications to the radiotelephones over a second range of satellite band forward link frequencies that is spaced apart from the first range, in a first mode of operation. In a second mode of operation, the multiple mode ancillary terrestrial component is configured to receive wireless communications from the radiotelephones over at least a subset of the second range of satellite band forward link frequencies and to transmit wireless communications to the radiotelephones over at least a subset of the first range of satellite band return link frequencies that is spaced apart from the second range. Thus, standard and reverse frequency modes may be provided. In other embodiments, in the second mode of operation, the ancillary terrestrial component is configured to receive wireless communications from the radiotelephones over all of the second range of satellite band forward link frequencies and to transmit wireless communications to the radiotelephones over all of the first range of satellite band return link frequencies that is spaced apart from the second range. Thus, the entire forward and reverse frequency bands may be interchanged by the ancillary terrestrial component.
It will be understood by those having skill in the art that the above embodiments have been described primarily with respect to multiple mode ancillary terrestrial components. However, a single mode ancillary terrestrial component also may be provided that can only include the second modes that were described above. Moreover, some or all of the various embodiments described above may be combined in embodiments of a multiple mode or single mode ancillary terrestrial component. Also, although the embodiments described above have been described primarily with respect to ancillary terrestrial components, analogous method embodiments also may be provided. Finally, analogous multiple mode or single mode radiotelephones that can interface with a space-based component and/or with the analogous embodiments of the multiple mode or single mode ancillary terrestrial components also may be provided. Accordingly, satellite frequencies may be reused terrestrially, to allow improved reliability, capacity, cost effectiveness and/or aesthetic appeal and/or to reduce or eliminate interference with other satellite-based systems such as GPS/GLONASS.